Nanomedicine is an emerging area of medicine that utilizes nanoparticles for the detection and treatment of various diseases and disorders. Nanoparticles are tiny fragments of metals (or non metals) that are 100,000 times smaller than the width of human hair. Nanoparticles typically have different properties than naturally occurring bulk materials. Collateral properties emanate when materials, especially metals, are reduced to dimensions measured in nanometers. Nanoparticles exhibit properties that are unique from their corresponding naturally occurring bulk material.
Nanoparticles within the size range of about 1-50 nanometers have a size that can be correlated to cells, viruses, proteins and antibodies. The size resemblance that such nanoparticles have to living cells and cell components are of great interest to medical research because cells are primary components of all life (humans and animals).
Gold nanoparticles have a number of important potential medical applications. One application is hyperthermia treatment in which gold nanoparticles are heated with oscillating magnetic fields after being associated with a targeted cell, typically cancer cells. Other applications relate to biological imaging, as gold nanoparticles display photo absorbance or emission characteristics that can be used in imaging for the diagnosis of various diseases. Contrast enhancement is also provided by gold nanoparticles. For example, the selective absorption of X-rays by gold and other metallic nanoparticles provides measurable contrasts for use in computer tomographic (CT) imaging and other imaging techniques These and other important diagnostic and therapeutic properties are attainable only when metallic (or non metallic) materials are reduced to nanometer particle sizes.
Gold nanoparticles have unique properties that make them more attractive than other nanoparticles for many therapeutic, imaging, and sensing applications, and particularly in medical applications. Gold nanoparticles have an unoxidized state, whereas most of the surface of less noble metals get oxidized to a depth of several nanometers or more, often significantly reducing or obliterating the nanoscale properties of the nanoparticles. Gold nanoparticles are highly reactive, but biocompatible, making them especially well-suited for in vivo imaging and therapy. Gold nanoparticles can also be coated with specific biomolecules including, monoclonal antibodies, aptamers, peptides and various receptor specific substrates. Receptor specific coated nanoparticles are used mainly for targeting three different markers that are over expressed on cancer cells. They include: matrix metalloproteases, epidermal growth factor receptor, and oncoproteins that are associated with human papillomavirus infection.
For such in vivo imaging and therapy applications, it is that gold nanoparticles be produced stabilized in a biologically benign medium. Many current methods of producing gold nanoparticles require the removal of unreacted chemicals and byproducts from the nanoparticles as the chemicals and byproducts are necessary to the synthesis of the gold nanoparticles. The chemicals and byproducts must be removed after the production of nanoparticles to make the nanoparticles biocompatible.
Typical known methods of making nanoparticles utilize harsh conditions, such as the application of sodium borohydride to reduce AuCl4−. See, e.g., M. Brust et al, “Synthesis of Thiol-Derivatized Gold Nanoparticles in a 2-Phase Liquid-Liquid System” Journal of the Chemical Society-Chemical Communications (7):801-02 (1994). The method provides for the efficient production of gold nanoparticle, but is unsuitable in the presence of target specific peptides because sodium borohydride will reduce chemical functionalities present on peptide backbones, which can reduce or eliminate the biospecificity of biomolecules. The sodium borohydride reduction method also uses thiols to stabilize the gold nanoparticles from agglomeration. Thiol-gold nanoparticle interaction is strong and makes gold nanoparticles highly stable. Once the gold nanoparticles are stabilized by thiols, they cannot be readily transferred onto useful drug moieties including peptides, proteins and various biochemical vectors that are normally used to target diagnostic and therapeutic gold nanoparticles on to tumor and various disease sites in the body. Other methods that have been developed utilize chemical cocktails during nanoparticle production, and are not environmentally friendly in additional to having the drawbacks concerning stabilization, reactivity, and biocompatibility.